diff --git a/2023/src/bin/day13.rs b/2023/src/bin/day13.rs
index 0459120..90e4420 100644
--- a/2023/src/bin/day13.rs
+++ b/2023/src/bin/day13.rs
@@ -3,13 +3,16 @@ extern crate test;
 use aoc2023::{boilerplate, common::*};
 
 const DAY: usize = 13;
-type Parsed = Vec<Vec<Vec<bool>>>;
+type Parsed = Vec<Vec<I>>;
+type I = u32;
 
 fn parse_input(raw: &str) -> Parsed {
-    raw.split("\n\n").map(|block| block.lines().map(|l| l.bytes().map(|b| b == b'#').collect()).collect()).collect()
+    raw.split("\n\n")
+        .map(|block| block.lines().map(|l| l.bytes().map(|b| b == b'#').fold(0, |acc, n| (acc << 1) | n as I)).collect())
+        .collect()
 }
 
-fn find_reflection(block: &[Vec<bool>], blacklist: Option<usize>) -> Option<usize> {
+fn find_reflection(block: &[I], blacklist: Option<usize>) -> Option<usize> {
     'outer: for i in 0..block.len() - 1 {
         let mut offset = 0;
         loop {
@@ -30,12 +33,15 @@ fn part1(blocks: &Parsed) -> usize {
         .sum()
 }
 
-fn transpose(orig: &[Vec<bool>]) -> Vec<Vec<bool>> {
-    let mut out = vec![vec![false; orig.len()]; orig[0].len()];
-    for i in 0..orig.len() {
-        #[allow(clippy::needless_range_loop)]
-        for j in 0..orig[0].len() {
-            out[j][i] = orig[i][j];
+fn transpose(orig: &[I]) -> Vec<I> {
+    let max = orig.iter().max().unwrap();
+    let len = (I::BITS - max.leading_zeros()) as usize;
+    let mut out = vec![0; len];
+    for j in 0..len {
+        for (i, &value) in orig.iter().enumerate() {
+            if (value & (1 << j)) != 0 {
+                out[len - 1 - j] |= 1 << (orig.len() - 1) >> i;
+            }
         }
     }
     out
@@ -49,17 +55,19 @@ fn part2(blocks: &Parsed) -> usize {
             let mut transposed = transpose(&block);
             let p1 = find_reflection(&block, None).map(|n| n - 1);
             let p1_transposed = find_reflection(&transposed, None).map(|n| n - 1);
+            let max = block.iter().max().unwrap();
+            let len = (I::BITS - max.leading_zeros()) as usize;
             for i in 0..block.len() {
-                for j in 0..block[0].len() {
-                    block[i][j] ^= true;
-                    transposed[j][i] ^= true;
+                for j in 0..len {
+                    block[i] ^= 1 << j;
+                    transposed[j] ^= 1 << i;
                     if let Some(reflection) =
                         find_reflection(&block, p1).map(|n| n * 100).or_else(|| find_reflection(&transposed, p1_transposed))
                     {
                         return reflection;
                     }
-                    block[i][j] ^= true;
-                    transposed[j][i] ^= true;
+                    block[i] ^= 1 << j;
+                    transposed[j] ^= 1 << i;
                 }
             }
             unreachable!()
@@ -94,7 +102,24 @@ boilerplate! {
             TEST_INPUT_VERTICAL => 300,
         },
     },
+    unittests: {
+        transpose: {
+            &[
+                0b100,
+                0b010,
+            ] => TRANSPOSE_42,
+            &[
+                0b101,
+                0b010,
+            ] => TRANSPOSE_52,
+        },
+    },
     bench1 == 37561,
     bench2 == 31108,
     bench_parse: Vec::len => 100,
 }
+
+#[cfg(test)]
+const TRANSPOSE_52: &[I] = &[0b10, 0b01, 0b10];
+#[cfg(test)]
+const TRANSPOSE_42: &[I] = &[0b10, 0b01, 0b00];